1. Field of the Invention
This invention relates to a valve assembly for a fluid-containing tank and method of making same and in particular to such a valve assembly which is bottom operable and is particularly adapted to be used on such a tank of a railway tank car.
2. Description of the Prior Art
The Association of American Railroads (AAR) and Department of Transportation (DOT) have railway tank car regulations which require that projections extending in excess of one inch below the bottom of the tank of such a car must be protected by a skid, or if such a projection is part of a valve assembly associated with the tank car it must be capable of being sheared away without affecting the integrity of such valve assembly. In instances where a skid is provided the skid must be in the form of a ramp having a longitudinal dimension along the bottom of the tank which is three times the dimension projecting downwardly from such bottom. In an effort to comply with the above-mentioned regulations, various valve assemblies have been proposed heretofore for use on such tank cars; and, a typical valve assembly which has a skid defined as an integral part thereof is disclosed in U.S. Pat. No. 4,234,158.
It is also known in the art to provide a bottom operable valve assembly for a railway tank car and examples of such a valve assembly are disclosed in U.S. Pat. Nos. 3,721,424, 4,212,447, and 4,318,531.
It has also been proposed heretofore to provide a valve assembly for a tank of a railway tank car wherein such valve assembly is both top operable and bottom operable and typical examples of such a valve assembly are disclosed in the U.S. Pat. Nos. 4,280,679 and 4,313,591.
It is also known in the art to provide a so-called plug valve assembly which is usable on a railway tank car, and an example of such a plug valve assembly is illustrated in U.S. Pat. No. 3,442,490. Further, such a plug valve assembly may have means which operates independently of the seal means for the plug member thereof for controlling the leakage past the actuating stem for such plug member.
It is also known to provide a plug valve assembly wherein the plug member thereof has a reverse taper therein, i.e., the taper of the plug of such a valve is toward the actuating stem instead of away therefrom as is typical of most plug valves, and such a valve is disclosed in U.S. Pat. No. 3,263,697. Also, in the valve disclosed in this last-mentioned patent, the actuating stem of such a valve is not axially coupled to the plug.
Finally, it is well known in the art to provide so-called ball valves for various applications; and, because such ball valves are so well known, particular examples of ball valves will not be presented herein.
However, each of the above-mentioned valve assemblies and/or valves is deficient as a valve assembly for a fluid containing tank of a railway tank car in one or more of the following respects in that each valve assembly does not comply with AAR and/or DOT railway tank car regulations or if it complies with such regulations requires comparatively expensive skid means in association therewith which add to the cost of the overall valve assembly, does not provide for complete drainage of all the fluid in its associated tank, or has no provision for substantially free unobstructed flow of fluid through the valve with minimum pressure drop through such valve from the inlet through the valve closure element to the outlet thereof in a rectilinear path.